In July 2003, Rick Anthes responded to a request
from Senator John McCain (R-Arizona) for information relevant to the McCain-Lieberman
Climate Stewardship Act (S. 139). Here is the full text of Dr. Anthes' response.

July 29, 2003

The Honorable John McCain
United States Senate
241 Senate Russell Office Building
Washington, D.C. 20510

Dear Senator McCain:

In response to your letter of July 28, 2003, I would like to offer the following
responses to your questions regarding the science of climate change. Your original
questions are included in italics:

Question 1 -- First, is there a scientific consensus in your atmospheric
research community that the earth has been experiencing a warming trend in the
last century and that this global climate change would not be expected from
the study of climate changes that have occurred in past millennia? What modeling
or other evidence supports your conclusion?

There is strong agreement among the vast majority of climate scientists that
Earth has been experiencing a warming trend in the last century and that this
global climate change would not be expected from the natural variability such
as that experienced in past millennia. By climate scientists, I mean scientists
who are actually doing climate science, either modeling or observations, and
publishing their work in peer-reviewed professional scientific journals. The
enclosed article, On Past Temperatures and Anomalous
Late 20th Century Warmth, appeared very recently in the scientific publication,
Eos, of the American Geophysical Union. The authors are thirteen highly
respected scientists from diverse institutions who answer your question unequivocally
in the following statement: " the conclusion that late-20th century
hemispheric-scale warmth is anomalous in the long-term (at least millennial)
context, and that anthropogenic factors likely play an important role in explaining
the anomalous recent warmth, is a robust consensus view." The article also
provides references to independently developed global climate models from different
institutions (e.g. the National Center for Atmospheric Research, the Geophysical
Fluid Dynamics Laboratory, the Hadley Centre in the U.K.) that all demonstrate,
"that it is not possible to explain the anomalous late-20th century warmth
without the contribution of anthropogenic factors."

It is noteworthy that the very recent document, The U.S. Climate Change
Science Program-A Vision for the Program and Highlights of the Scientific Strategic
Plan, which was transmitted to Congress by the highest levels of the Administration,
prominently features a quote from the June 2001 NRC report, Climate Change
Science: An Analysis of Some Key Questions: "Greenhouse gases are accumulating
in Earth's atmosphere as a result of human activities, causing surface air temperatures
and subsurface ocean temperatures to rise."

The best evidence for a scientific consensus is the Intergovernmental Panel
on Climate Change (IPCC) process, which is open to all, and all comments are
dealt with and addressed with a written record. Skeptics are involved both as
authors and reviewers. I know that you are familiar with the IPCC Third Assessment
Report. I want to endorse the conclusions of the report as representing the
best, most accurate science that the resources of countries around the world
are able to produce. Approximately 700 scientists worldwide contribute to the
IPCC reports, and another 700 review them. The fact that this number of scientists,
working directly in the field of climate and climate change, produce a consensus,
policy-neutral document like the IPCC Third Assessment Report of Working Group
1 is an extraordinary achievement in itself and is likely without parallel in
any other field of research.

The main observations of the IPCC Report lead, correctly in my view, to the
conclusion that the global average surface temperature has increased over the
20th century by about 0.6 degree Centigrade (1.1 degree Fahrenheit), that the
increase in temperature in the late 20th century over the Northern Hemisphere
is the largest of any century in the past 1,000 years, and that human activity
has caused a major percentage of that late century warming. The warming of the
planet has caused snow cover to decrease, glaciers to retreat, global average
sea level to rise, and ocean heat content to increase. We are entering a climate
regime never before experienced by human civilization.

Question 2 -- Second, is the scientific community in agreement that
this climate change is due to the accumulation of enormous quantities of greenhouse
gases in the atmosphere due to human activities, primarily the burning of fossil
fuels?

Yes, as answered above. This is now very widely believed to be so, even among
many skeptics, some of who now argue that the warming will be benign. As noted
above, it is not possible to explain the anomalous late-20th century warmth
without the contribution of anthropogenic factors.

Question 3 -- Third, does the scientific evidence point to the need
to take measures to reduce greenhouse gas emissions now and the potential consequences
of inaction?

This question is a lot tougher because it brings into play non-scientific issues
and issues that I am not an expert in such as economic and other social factors.
However, my personal opinion is that we should not wait to act until
everything is known about all of these complex issues. The risk of climate change
is very real and the peoples of the world, including those in the United States,
should adopt a "no-regrets" strategy and take a number of actions
to reduce the threat. This would include stabilizing the global population,
reducing fossil fuel emissions, emphasizing conservation much more than we do
now, developing alternative and renewable energy sources, and many other actions.
In my opinion, these actions would be beneficial even without climate change.
I believe we can do all of these things without reducing our standard of living.
In fact, I believe that we can do these things and actually increase the quality
of life in this and other countries.

In my judgment we should, as a nation, show leadership in this area and act
not only to reduce the risk, but also to prepare for the unprecedented changes
that are already likely to occur because of humanity's previous actions. This
is the responsible course of action. Major disruptions to the U.S. agriculture,
economy, and quality of life due to imminent climate change are definitely possible,
if not likely. And the threat is not just short term; there are very long time
scales involved. For example, concentrations of greenhouse gases take 50 or
more years to change perceptibly because they depend on accumulated emissions.
The oceans respond to atmospheric heating sluggishly and add a delay of 20 years
or more, and ice sheets respond on a much longer timescale. Sea level will take
centuries to reach a new equilibrium.

Hence, if we wait for proof beyond a shadow of a doubt that the climate has
changed for the worse, it will be much too late to do anything about it.

One of the main risks for the United States is that of a massive, persistent
drought. As we know from paleoclimate records, such droughts have occurred in
the past. Imagine the Dust Bowl in the 1930s, but lasting for many decades,
perhaps centuries, and covering most of the nation, from the West Coast to the
Mississippi. This is a real risk, especially because of the likelihood of summer
continental drought, which is exacerbated by diminished snow pack in spring.
Such a change could occur abruptly and would be devastating for the U.S. As
you know from the situation in your own state, such drought has been persistent
in the Southwest during the past two years, with consequences for water supplies,
heat waves and wild fires.

In summary, prudence (the precautionary principle) argues that we should make
an honest and good faith effort to slow the rate of change as well as prepare
for changes that are likely to occur even if we start acting now. We are entering
into the unknown; we have good guesses as to what may occur, but our knowledge
is not enough to make really good predictions. I cannot say with certainty that
any of the catastrophic changes suggested by many climate models and the paleoclimate
record will occur, but likewise nobody can say with any certainty whatsoever
that they will not occur. Again, prudence and risk reduction are called for
given the scientific evidence that we now have.

I hope the research information and the personal opinions I have offered are
of some relevance and assistance as you and Senator Lieberman offer your amendment
to the Senate energy bill.